Regarding an insulated wire obtained by extrusion-coating a linear polyester resin composed of an aromatic dicarboxylic acid residue and an aliphatic glycol, such as a polyethylene terephthalate resin (hereinafter, referred to as PET) or a polybutylene terephthalate resin, if the insulated wire is left under the environment of a temperature at 30° C. or more, degradation of dielectric breakdown voltage caused by occurrence of crazing is confirmed. As means for solving this problem, there is proposed that a stable dielectric breakdown voltage of an insulated wire is obtained, by blending 1 to 15% by mass of an ethylene-series copolymer containing a carboxylic acid having good compatibility with the polyester-series resin.
However, with the recent tendency of the miniaturization of electric and electronic machinery and tools, there is a need for improvement of electric insulation properties under high-temperature environment as heat generation or heat release properties are deteriorated due to their components. With respect to this, an insulated wire obtained by extrusion-coating a conventional polyester resin cannot sufficiently satisfy the above need.
Other and further features and advantages of the invention will appear more fully from the following description.